A number of testing procedures exist to determine the safety of consumer products and other materials with respect to human skin and eyes. Skin and eye safety data are required by various government agencies for many types of materials. Even when not mandated by law, most companies conduct tests to ensure the safety of many types of products.
A number of methods are known in the prior art and employed for estimating dermal and ocular corrosivity of products. Quite commonly such tests involve the use of live animals, primarily white albino New Zealand rabbits.
Problems inherent in animal testing include intra-laboratory variability in scoring and handling, variation in individual rabbit (or other animal) responses, variation in application of test compound and occlusive seal, and variation in sex and age of animals. In addition, the most common animal tests tend to overpredict corrosivity as applied to humans. Some persons criticize the use of animal testing in general on moral or ethical grounds.
Computer modeling has also been employed in some instances as a predictive tool for toxicology. Modeling has only been successfully used for a very few specific applications and only predicts corrosivity/irritation, not the degree thereof.
Diffusion tests utilizing excised animal skin or corneas has also been employed. In such tests, permeability is measured through skin or cornea. One test involving bovine ocular and cornea permeability utilizes a two chamber apparatus wherein one chamber contains a material such as a detergent solution or other compound and the other chamber contains a dye. The dye transfer through the cornea is observed and follow-up pathology measurement of the cornea cells takes place as well. Utilizing this approach, animals are destroyed and animal to animal variability adversely affects the accuracy of the test.
Another prior art test is based on the cytotoxicity of cultured cells. In this approach cells are exposed to solutions or individual compounds for a specified period of time. Dye is then applied which is absorbed into dead or ruptured cells. The effect of the dye on the cells is evaluated visually. This test does not continuously measure the rate at which cellular material is destroyed or the rate that cleaning compounds or other materials adsorb to cellular material during the corrosion process.
Another known approach involves synthetic biomembrane analysis. Biomolecules which make up biomembranes have been studied for skin corrosivity generally for many years and a relationship exists between soap and detergent denaturing and swelling of keratin, the primary protein found in skin, and in vivo dermatitis. These techniques are much like those employed in the cytotoxicity studies discussed above and involve evaluating the biomolecules under a microscope one by one following exposure.
U.S. Pat. No. 5,411,888, issued May 2, 1995, discloses a non-animal testing approach for the measurement of corrosivity of chemicals which essentially is an expansion or elaboration of the biomembrane technique just described. In one approach disclosed in the patent, corrosivity is evaluated by measuring the time required for the test substance to transit a biobarrier that mimics human skin or membranes or the time required to cause a component of such biobarrier to break down and transit the membrane. The invention also envisions alternative approaches which involve series of layers of dyes and corrosive-resistant materials coated onto microspheres or test strips.
The biobarrier suggested by U.S. Pat. No. 5,411,888 is comprised of keratin that has been dissolved in ethylene glycol and cellulose or other materials. While the patent discloses cholesterol as an optional ingredient, it does not disclose how one would make a biomembrane that includes cholesterol or any phospholipids. The test cannot readily distinguish between rapid reactions and distinctions in reaction speeds are critical to the design of safer consumer products and other types of materials, insofar as ocular and skin corrosivity is concerned. Also, ethylene glycol, cellulose and other materials employed in the test may have interfering side reactions with chemicals under study.